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Emulator Bugs (Alleyway & Volley Fire)
http://forums.nesdev.com/viewtopic.php?f=20&t=14608
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Author:  breathermachine [ Wed Aug 03, 2016 9:03 am ]
Post subject:  Emulator Bugs (Alleyway & Volley Fire)

I have bugs emulating Alleyway & Volley Fire.

For Alleyway, the game auto starts by itself and proceeds to the game. However, I cannot move the paddle and it is stuck all the way to the left.

For Volley Fire, the rocks don't move. From my observations, the game is not using HBLANK STAT interrupts. I have also observed that SCX remains at 0.

Thank you.

Author:  binji [ Wed Aug 03, 2016 2:55 pm ]
Post subject:  Re: Emulator Bugs (Alleyway & Volley Fire)

I haven't tried Volley Fire, but IIRC Alleyway did the same thing for me. Adding some basic serial port emulation fixed it. You don't need to actually implement it fully; in my case, I just always have the remote end send 0xff, which AIUI is the value that means that the remote end is not connected.

Author:  breathermachine [ Wed Aug 03, 2016 3:45 pm ]
Post subject:  Re: Emulator Bugs (Alleyway & Volley Fire)

Implementing a bare-bones serial fixed it. I was missing serial interrupts and was not getting any read requests from $FF01.

Thanks!

EDIT: This also fixed the rock scrolling in Volley Fire, although I'm having one scanline graphical glitches of the rocks.

Author:  binji [ Thu Aug 04, 2016 9:59 am ]
Post subject:  Re: Emulator Bugs (Alleyway & Volley Fire)

Just tried Volley Fire, and I see the occasional 1-pixel glitch on the top of the rocks too. It seems to be using the LY=LYC STAT interrupt to do the scrolling rocks, which are in the BG, not sprites. I'm guessing my interrupt is off a little bit, I've seen similar issues in Super Mario Land with the very first line of the status occasionally being wrong too.

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